| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1988: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1987: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
It is well known that roughening the surface by use of turbulence promoters (regular geometric toughness element) on the wall surface in a duct improves the heat transfer from the wall.
It is effective to produce high geat transfer coefficients to make high efficiency heat exchanger. Liquid(high Prandtl's fluid) such as water obtained high heat transfer coefficients is effective, comparing with air (low Prandtl's fluid) as used fluid. Further, in order to obtain high efficiency, passive heat transfer enhancement technique which tubulence promoters is installed on the wall in a duct is adopted and the mechanism of the enhancement is experimentally studied.
In experiment, electrolyte solution (high Prandtl,s number) as the fluid and three kinds of turbulence promoter as the shape of the promoter are used. Mass transfer coefficients were measured by using a redox reaction on the wall. Heat transfer enhancement were obtained by comparing with the ratio of the case without promoters. In order
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to solve the mechanism of the local enhancement, flow behaviour was qualititively observed by visualization ising aluminum powder tracer method, and velocity, shear stress and turbulence intensity profiles were quantitively measured by 2-channels hot wire anemometer. Both results were compared with each other and checked.
As results, though flow behaviour and velocity profile were different from a kind and a shape of turbulence promoter. Generally, in case of no clearance between the wall and the promoter, enhanced heat transfer was caused by the turbulence at reattachment flow region due to separated flow from the top of the promoter. In case of some clearances, the flow behaviour was also changed by the clearance but enhanced heat transfer was obtained at little down stream below the promoter and at 3 to 7 times of promoter length. It was found that tne mechanisms in two regions are ; former is due to a thin layer by the jet flow below the promoter and later is mainlydue to the turbulence by the fluid agitation, through the comparison of the turbulence intensity and the shear stress distribution.
Further, fluid friction factors were measured from the view points of energy saving and equipment performance was tried to accompany with the enhanced heat transfer. Less
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